1. Field of the Invention
The present invention relates to an adaptive variable-length coding apparatus for not only converting fixed length code words into variable-length code words, but also converting variable-length code words into fixed length code words.
2. Description of the Prior Art
Generally, variable-length coding is to compress image data so that the image data having a large bandwidth can be transmitted in a real time through a transmission medium having a small bandwidth. In accordance with such a variable-length coding, a code word having the minimum number of bits is allocated to source symbols frequently used, thereby enabling the bit rate of the source symbols to be reduced. Well-known variable-length coders are classified into variable-length encoders, in which source symbols are processed to correspond to variable-length code words, and variable-length decoders, in which source symbols corresponding to the variable-length code words are searched from a decoding tree. The variable-length encoders have a construction contrary to that of the variable-length decoders. Due to such a difference in construction, conventional variable-length coders could not be used both as an encoder and a decoder.
In cases of change and addition of source symbols or variable-length code words, the variable-length encoder and the variable-length decoder should be re-designed because they include look-up tables or programmable logic arrays. In a variable-length coder having a look-up table, the memory capacity is unnecessarily large because code words corresponding to the number of bits of source symbols must be stored in the memory.